WO1984001825A1

WO1984001825A1 - Inking system for producing circuit patterns

Info

Publication number: WO1984001825A1
Application number: PCT/US1983/001669
Authority: WO
Inventors: Carl E Drumheller
Original assignee: Microscience Systems Corp
Priority date: 1982-10-26
Filing date: 1983-10-21
Publication date: 1984-05-10
Also published as: JPS60500011A; CA1205569A; US4485387A; EP0126742A4; EP0126742A1

Abstract

Thick film inking system where circuit patterns are written by ink feed through an orifice of a writing pen (28). Line cross-section is controlled by synchronous positive displacement pumping (Fig. 3) of ink through the orifice with the motion of the substrate with respect to the pen. A dynamic pen control system provides spring and mass compensation and maintains positive, prescribed pen force on the extruding ink thereby maintaining the desired thickness to width ratio of the lines.

Description

- 1 -

INKING SYSTEM FOR PRODUCING CIRCUIT PATTERNS

Description

The present invention relates an orifice print¬ ing system which produces patterns by writing on a sub- 5 strate with inks which are dispensed through the ori¬ fice, and particularly to a writing system wherein inks are dispensed through a writing orifice to print thick film circuit patterns on a substrate.

The United States Government has rights in this 10 invention pursuant to contract N00163-79-C-0175 awarded by the Naval Air Systems Command.

The invention is especially suitable for use in a CAD/CAM (computer aided design - computer aided manu¬ facture) system for producing thick film circuit pat- 15 terns on insulating substrates, such as ceramic plates.

In the past most thick film circuit patterns were produced by screen printing through masks. The process of screen printing has been found time consuming and expensive. It is difficult to obtain repeatable and 20 uniform circuit performance particularly for circuits designed for high frequency applications. Earlier work on thick film printing involved the use of orifice writ¬ ing systems in which thick film inks are dispensed through a writing orifice to produce the lines making up 25 a circuit pattern on the substrate. With such orifice writing systems, however, it has been difficult to obtain controlled, uniform cross-section of inked lines and filled areas, particularly at different writing speeds.

30 It is a principal object of the present inven¬ tion to provide an improved inking system for producing

OMPI - 2 -

circuit patterns wherein ink is dispensed from an ori¬ fice writing pen which provides controlled, uniform cross-section of lines over a wide range of line width (e.g., four to twelve mils) and a wide range of writing speeds of relative movement of the substrate with respect to the pen (e.g., .05 to 5 inches per second) .

It is a further object of the present invention to provide improvements in thick film orifice printing technology which enables the production of long line lengths in various patterns as well as uniform fill in areas.

It is a still further object of the present invention to provide an improved inking system for pro¬ ducing circuit patterns in which the starts and termina¬ tions of lines are controlled to achieve uniformity of cross-section at both ends of the line as well as along the length of the line between the ends thereof.

It is a still further object of the present invention to provide an improved inking system for pro¬ ducing circuit patterns through the use of a pen with a writing orifice having interchangeable pen assemblies for handling a wide variety of conductor, dielectric and resistor inks, with interchangeable pen tips for dif¬ ferent line widths.

It is a still further object of the present invention to provide an improved inking system for pro¬ ducing circuit patterns which allows for variations in the camber of the substrate, as on crossovers of pre¬ viously written lines, without the need of outrigger or other surface contour following probes, and therefore is capable of producing various circuit patterns, even if convoluted and containing cross overs and closely adja¬ cent lines; thus providing for topology independence in inking sequence.

OMPI / IPO _ - 3 -

Briefly described a system for producing pat¬ terns on a substrate in accordance with the invention uses a member having an orifice (a writing pen) . The system includes means for moving the substrate with 5 respect to the pen. Means are provided for controllably feeding ink through the pen orifice at a volume rate synchronous with the rate of relative movement of the member and substrate. This system may also include means responsive to the viscous forces on the ink flow- 10 ing from the orifice upon the substrate which dynami¬ cally controls the vertical displacement of the pen to maintain a constant thickness of line in the pattern for a given cross-sectional area of the line.

The foregoing and other objects features and

15 advantages of the invention as well as presently pre¬ ferred embodiments thereof, will become more apparent from a reading of the following description in connec¬ tion with the accompanying drawings in which:

FIG. 1 is a block diagram of an inking system

20 provided in accordance with the invention showing, prin¬ cipally portions of the system concerned with synchro¬ nous positive displacement ink feed through the writing orifice of the pen used in the system;

FIG. 2 is a block diagram showing the pen used

25 in the system described in FIG. 1 as well as components thereof which provide for dynamic pen control based on sensing ink flow through the orifice at the pen tip; FIG. 3 is a perspective view schematically showing the mechanism of the inking system illustrated

30 in FIGS. 1 and 2, but with the sensors and actuators associated with the pen for dynamic pen control, which are shown in FIG. 2, removed, to simplify the illustration; - 4

FIG. 4 is an enlarged perspective vie showing the interchangeable pen assembly of the system shown in FIG. 3, the view being partially in section, the section being taken along the line 4-4 in FIG. 3; FIG. 5 is an enlarged fragmentary sectional view of the ram of the positive displacement pumping mechanism shown in FIG. 4, the section being taken in the general area of the circle indicated in FIG. 4 by the numeral 5, which numeral is contained in a balloon; FIG. 6 is an enlarged fragmentary sectional view illustrating the valve assembly used in the con¬ stant displacement pumping assembly shown in FIGS. 3-5, the section being taken along the line B-B in FIG. 7; FIG. 7 is an enlarged fragmentary sectional view of the valve assembly shown in FIG. 6, taken along the line A-A in FIG. 6;

FIG. 8 is a view of the valve assembly similar to the view of FIG. 7, and showing another embodiment thereof; FIG. 9 is a fragmentary elevational view of the pen, its lift mechanism and the electro-optical mecha¬ nism associated therewith for sensing the vertical dis¬ placement of the pen with respect to the substrate;

FIG. 10 is a schematic view of the vane used in the electro-optical assembly shown in FIG. 9, the view being taken along the line A-A in FIG. 9;

FIG. 11 is a schematic view illustrating the pen tip and substrate during initial ink flow from the writing orifice; FIG. 12 is a block diagram illustrating the portions of the inking system operative to control and maintain constant cross-section of line at starts and terminations of lines during the writing thereof, and

OMPI - 5 -

FIG. 13 is a timing diagram illustrating the operation of the portions of the system which are shown in FIG. 12.

Referring more particularly to FIG. 1, a system

5 is shown which may be used for the development of cir¬ cuit patterns for thick film hybrid circuits as well as for the computer aided manufacturer of such circuits.

The circuit is printed by writing the pattern on a substrate with standard thick film ink material.

1° The pen having the writing orifice and the mechanism for lifting and depressing the pen with respect to the sub¬ strate (an electromagnet coil) is shown in FIG. 2. The substrate 20 (FIG. 3) is mounted on an xy translator table 22 which is driven in the x direction by a motor

15 24 and in the y direction by another motor 26. These motors drive the table to obtain a desired tangential speed with respect to the pen tip having the writing orifice.

FIG. 1 shows the motor controller 29 for the x

20 motor 24 and the motor controller 30 for the y motor 26. Also shown is an ink pump motor 32 which is con¬ trolled by an ink pump motor controller 36. The motor controllers 28, 30, and 36 translate command pulses generated by a microprocessor interface controller 38

25 into signals which drive the motors. The number of pulses determines the displacement produced by the motors and the pulse rate determines the velocity of that displacement. The motors may be rotary motors with screw drives or other gearing to translate the rotary 30 motion to linear motion. Linear motors may also be used. A computer determines the pen path topology for the pattern which may consist of rectangles, paths, triangles and arcs for any chosen pen width. The com¬ puter date is transferred by way of a data bus (suitably

OMPI

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the IEEE-488 bus) to the controller 38. The computer is equipped with a keyboard 42 into which the operator can input the inking parameters, such as the cross-sectional areas of the lines which are to be written and the writ- ing speed of the pen. Circuit development can be accom¬ plished through the use of the keyboard together with other input devices such as a digitizer/tablet. The pattern may be displayed together with other information concerning inking parameters in alpha-numeric form on a graphics display such as a cathode-ray tube display 44. A printer with graphics display capability and a plotter may also be tied to the computer as peripheral devices. The pattern of the circuit may be created in the com¬ puter aided design operation of the system and stored on a disk or other storage medium 46. A floppy disk storage system using a disk drive 48 may suitably be connected to the computer as a peripheral device for reading and writing on the disks. The computer aided design aspect of the system may be carried out with techniques used in the art for computer aided design (CAD) purposes.

The pen 28 is part of an interchangeable pen- pump assembly 50. Several assemblies which contain a syringe 52, a positive displacement pump mechanism in a pump block 54, the pen tip 28 and a flexural, A-frame support 56 for the pen tip are provided. The pen tips may be ceramic, metal or plastic and have orifices of various size to change the line width when the pen tip is changed. The ink supply is from the syringe 52. The syringe of each interchangeable assembly 50 may be loaded with a different ink material. For example, con¬ ductor, dielectric and resistor inks may be loaded into the syringes of the various pen assemblies. Different

OMPI assemblies may be used for different resistor inks for different resistivities. Inks can be changed readily by interchanging the pen assemblies 50.

The syringes 52 are desirably loaded with ink under vacuum conditions to avoid the inclusions of air or other gas in the ink material. Inasmuch as the syringes 52 are airtight, the pen assemblies 50 can be stored in a loaded condition for long periods of time without affecting inking quality. A pneumatic piston 58 provides constant force via a coupling 60 to the plunger 62 of the syringe 52. The pump block 54 contains a double acting pump mecha¬ nism. A passage 64 from the syringe goes to a central valve opening 66. A cylindrical valve body 68 in the opening 66 provides a four-way valve which alternately directs the ink supply to different pump volumes 70 and 72 defined in a bore 84. The double acting pump has two rams 74 and 76 which displace the pump volumes alter¬ nately to pump ink through an outlet passage 78. The outlet passage 78 is in communication with a tube 80 which has a conduit for ink delivery to the pen 28. The other tube 82 of the A-frame 56 provides added flexural support for the pen 28.

The valve 68 has two positions 90 degrees apart so that the syringe fills one of the volumes 70 and 72 while one of the rams 74 or 76 is pumping ink out of the other volume to the pen.

The ram 76 is shown by way of example in FIG. 5. It is a rod which is disposed in the bore 84 in the pump block 54 which provides, in part, the pump volumes. A bleed port for air (not shown) may be pro¬ vided and opened during initial charging of each of the pump volumes with ink. After air is purged the bleed

CMPI Yv-i-O ports are closed. Seal arrangements, including retainer nuts 86 close the pump volumes with which the rams interact. Inasmuch as the ink is in a small closed pump volume 70 or 72 the displacement of the rams 74 or 76 provides a positive volume displacement of the ink from the pump block to the pen. It is desirable that a pressure relief valve be disposed in communication with the passage 78 so as to relieve the pressure in the pump volume which is being pumped in the event of a pen clog. Accordingly during inking, one side of the double acting pump is pumping ink hydraulically from one pump volume, while the other pump volume is being refilled pneumatically. As noted above, ink is delivered to the pen 28 through the pen support tube 80 by positive dis- placement of the small, closed ink volume. As will be described more fully below, this positive displacement is in synchronism with the table movement and thus with the tangential writing speed of the pen 28.

The valve is shown in greater detail in FIGS. 6 and 7. The valve body 68 is a cylinder, preferably made of plastic material such as Delrin which is filled with Teflon particles. The passages through the valve are provided by slots 90 and 92 in the valve body which are opposite to each other. These slots 90 and 92 are posi- tioned at 45° with respect to the bores providing the pump volumes 72 and 74 as shown in FIG. 6. By turning the valves 90° from what is shown in FIG. 6 the pump volume 72 may be connected to the syringe delivery passage 64, while the pump volume 74 is connected to the pen delivery passage 78. A coupling 94 in the form of a pin 96 passing through the head of the valve body 68 is provided for rotating the valve body 90°.

The valve body 68 is undercut at 67 to form a step. A valve pin retainer plate 69 has its forward end

CMFI in the undercut and holds the valve body in place in the pump block 54 while allowing the valve body to rotate.

It has been found desirable that the valve be a zero clearance valve to prevent a flow of ink between the pump volumes 72 and 74 at the high pressures generated in the pump block. A zero clearance also assists in preventing the abrasive particles commonly found in thick film ink material from penetrating into the interface between the valve body 68 and the opening 66 in the block 54. Seals 98 and 100 held down by seal retainer nuts are disposed on the opposite sides of the passages 64, 72, 74 and 78 in the pump block 54. In order to facilitate obtaining a zero clearance valve, a tapered opening is provided axial in the valve body 68. A tapered pin 104 is inserted into this opening and spreads the plastic material of the valve body 68 to provide the zero clearance fit. Alternatively, and as shown in FIG. 8, a threaded tapered aperture 106 in which a threaded tapered pin 108 is screwed may be used to provide the adjustment for zero clearance fit. While Delrin AF filled with Teflon is presently preferred for use as the valve body other materials such as nylon.

Teflon and other phenolic resin plastic materials may be found suitable. As shown in FIG. 4 the pump block 54 has bores above and below the central level of the block in which the passages 64 and 78 and the pump volume 74 and 72 are disposed. Rods 110 and 112 are located in these bores. These rods 110 and 112 join the two double acting rams 74 and 76 together through coupling blocks 114 and 116 so that they act in concert as a double acting pump. A single drive rod 118 is used to drive both rams via the couplings 116 and 114 and the tie rods 110 and 112. The

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OMPI coupling 116 may have a quick disconnection so that the assembly 50 can be interchanged with like assemblies carrying different inks.

The motor 32 turns a drive screw 120 through a preloaded angle contact bearing set 124. The rotary motion of the drive screw 120 is converted into linear motion of the pump drive shaft 118 by a driven nut, ball slide arrangement 126. The position of the pump is sensed by a linear position transducer 128 which may be a linear potentiometer which is coupled to the linearly moving part of the driven nut ball slide arrangement 126. As shown in FIG. 1, the transducer 128 provides an output to the microprocessor interface controller 38 indicating the position (displacement) of the pump. The microprocessor interface has stored therein data repre¬ senting the total line length and ink volume necessary to complete the writing the next anticipated line in the pattern. If the position transducer indicates, that the remaining displacement volume is insufficient to com- plete the next anticipated line of the pattern, an out¬ put is provided to a controller 130 (see FIG. 1) from the microprocessor interface controller. This con¬ troller outputs drive current to an ink valve actuator 132 utilizing opposed solenoids 132 and 134 which recip- rocate a rack 136 to drive a spur 138 90° so as to turn the valve body 68. Accordingly when the double acting pump is reversed by signals applied to the ink pump motor 32 via the ink pump motor controller 36, the ink will be pumped from the recharged pump volume and the previously used pump volume will be placed in communica¬ tion with the syringe for recharging. Other actuators may be used for the ink valve, such pneumatically con¬ trolled cylinders.

G PI

^ ° Synchronous positive displacement pumping which assures controlled, uniform cross-section of ink lines and filled areas of the pattern, independent of selected writing speed, which may be up to 5 inches per second in this illustrated embodiment of the invention, is obtained by the conjoint control of the ink pump motor controller 36 and the x and y motor controllers 28 and 30. Consider by way of an example a selected writing speed (speed of relative motion of the pen with respect to the moving substrate on the table) of 2 inches per second and a cross-sectional area of line of 40 x 10 square inches. The ink motor 32 advances approximately 7.8 microinches, in this example, for each pulse which is applied to the ink pump motor controller 36. The geometry of the pump volumes 72 and 74 are such that a certain volume of ink will be displaced for each 7.8 microinch advance of the ram. In this example the pump volume geometry is such that the volume of ink displaced is 1.64 x 10 —8 cubic inches per pulse applied to the ink pump motor controller. At a 2 inch second writing

_7 speed and with a 40 x 10 inch cross-section of the line to be written, the ink volume requirements are the

_7 product or 80 x 10 cubic inches per second. Since

—8 1.64 x 10 cubic inches per pulse will be delivered

_7 by the pump, for an 80 x 10 cubic inches per second volume requirement to be achieved, the pulse rate must be 487.8 pulses per second. A simple algorithm is the interface controller 38 provides the necessary pulse rate with the known constant volume displacement of the pump and the desired parameters as inputted from the computer 40 (e.g., line writing speed and cross-section) .

Referring to FIG. 2 there is shown the pen with its pen tip 28 supported by the flexural support pro¬ vided by the ink and pen support tubes 56. The pen is

OMPI lifted and depressed with respect to the substrate 20 by an electromagnetic coil or solenoid on a core which is of low and preferably zero remnance. This core may be highly purified iron or suitable ferrite ceramic mate- rial. The actuation force is applied against a high coercivity magnetic material suitably a samarium cobalt magnet which opposes a non-magnetic spacer at the lower end of the core. A control signal from the microproces¬ sor generates a pen up/down command to a summing ampli- fier 140 which drives the electromagnet coil through a driver amplifier 142. When the pen up signal is asserted, the energizing current in the coil is increased and the magnet attracted to lift the pen up from the substrate. The magnet is lifted into contact with the spacer. Upon pen down command the current in the coil is reduced gradually to allow the pen tip to descend slowly for a soft landing on the substrate. Then the appropriate inputs are applied to the summing amplifier to establish the necessary magnetic force on the pen tip for dynamic pen control.

The dynamic pen control requires that the ver¬ tical position of the pen be sensed continuously. This accomplished by an electro-optical sensor using a source of illumination and a light detector. The illuminating source is suitably a light emitting diode (LED) opera¬ tive in the infra-red. The light detector is suitably an infra-red responsive photo transistor. A vane car¬ ried by the flexural support tubes 56 intercepts the beam of infra-red illumination. The amount of the beam which is intercepted and the amplitude of the illumina¬ tion detected by the photo transistor is proportional to the position of the vane and therefore of the vertical displacement of the pen tip 28. A square wave driver

OMPI / WIPO _ 144 and a synchronous detector 146 are used much in the same manner as in linear analogue optical switches to provide the pen height signal (d) . This pen height signal (d) is therefore an analogue signal the amplitude of which is directly proportional to the vertical dis¬ placement of the pen tip. Other displacement sensors, for example with Hall effect devices may be used. The electro-optical sensor is, however, preferred.

A vertical position meter 148, suitably a zero center meter, calibrated to zero at the center of the dynamic range of the sensor system (including the driver 144, detector and photo transistor, LED arrangement) . The meter thus enables monitoring visually the vertical position of the pen tip with respect to the center of the dynamic range. A microscope therefore need not be used in the setup adjustments of the writing system. Referring to FIGS. 9 and 10, it will be seen that the sensor is mounted in a bracket 150 closely adjacent to the electromagnetic coil. The vane 152 is shown mounted on the pen support tubes 56 in a first position at 154 where it is in writing relationship with the substrate and in a second position at 156 where it is lifted to the pen up position; the magnet being in contact with the non-magnetic spacer, as is the condition during loading new substrates and entering of data into the computer. The vane 152 has an aperture 158. It will be noted that in the writing position at 154, the beam 151 of illumination is partially blocked by the vane. Also in the up position as shown at 156 the beam 151 is also partially blocked, even though the optical sensor is not being used when the pen is in the pen up position. The passage of illumination through the aperture 158 in the pen up position maintains continuity of illuminating energy on the junction of the photo transistor. The temperature of the junction thus is maintained and thermal drift errors in the pen height signal at the beginning of inking when the pen is brought down towards the substrate are minimized.

Returning to FIG. 2 and also to FIG. 11, the operation of the system upon initial ink flow is illus¬ trated. Upon start of line, the pen tip 28 is allowed to drop into contact with the substrate 20 as above dis- cussed. FIG. 13 also shows the process. The pen lift signal which has actuated the electromagnet to hold the pen tip up against the non-magnetic spacer drops in amplitude. The vertical pen position thus changes as the pen reaches the substrate. After a suitable set- tling delay and indicated on the vertical pen position diagram as SMP a sample of the pen height signal is taken and held as in a sample and hold circuit. But this sample and hold circuit is contained in the ink flow sensor 160 (see FIG. 12.) The flow of ink is started by the application of the pulses which control the ink pumping through the ink pump motor controller 36 (FIG. 1) . Pumping of ink is initiated at a pre-pen lift pumping rate which may be different from the pumping rate used during inking of the line which is commanded by the computer so as to maintain uniformity of cross- section of line at different writing speeds. As the ink begins to flow, the viscous forces of the extruding ink, as shown on the right in FIG. 11 causes the pen 28 to rise. The pen height signal which represents the verti- cal pen position increases. When that signal reaches a preset level relative to the level at the sampling time, SMP, information is obtained for starting the table motion and also for increasing the pressure to provide - JL5 -

immediate compensation for the stored energy compression in the ink. Functionally, the ink flow sensor 160 (FIG. 12) provides an output when the relative amplitude of the vertical displacement signal reaches the threshold level to trigger a control signal generator 162. The trigger point, TR, is indicated in FIG. 13 on the vertical pen position diagram. The control signal generates a pulse, the duration of which may be set under operated control (the operator providing a control signal OP,) . This control signal is applied to a pumping rate pulse generator 166 in the interface con¬ troller 38 which then increases the pulse rate to the ink pump motor controller 36. The end of the control signal pulse is detected by an end of control signal detector 164 which responds to the lagging edge of the control pulse. This end of control signal enables the generators 168 and 170 which generate the speed control pulses for the x motor and y motor controllers 28 and 30. The table motion pulses which go these controllers 28 and 30 and then start as shown in FIG. 13. Also a level changer 172 is enabled to apply the pen force signal to the pen lift solenoid controller 174. This solenoid controller is provided by circuits in the sum¬ ming amplifier 40 and by the driver amplifier 142. This enables the pen force signal as inputted from the com¬ puter to be applied to the electromagnet coil. This pen force signal plays a part in the dynamic control of the vertical displacement of the pen as will be discussed below. Inasmuch as an appropriate pumping rate is selected at line start to overcome ink compression, the line which is written is uniform at line start as well as throughout the writing of the line. The system also accommodates for the energy in the ink upon termination of the line.

OMPI

, Wi?o Before discussing the operation of the system upon line termination, the dynamic pen control during the writing of the lines will be considered. This dynamic pen control is based on direct ink sensing by the pen tip 28 itself, and provides pen tracking of any substrate camber or cross-over contour without the use of a surface sensing "outrigger" probe at the pen tip. The electro-optical sensor monitors vertical pen tip location and exerts appropriate magnetic feedback forces via the summing amplifier and driver amplifier 142 on the pen tip 28. The feedback system electronically eliminates the spring constant of the pen tip supporting and ink feed structure. It also provides appropriate acceleration assist forces to reduce the inertia of the pen tip. A suitable design may have an operating band width of 200 hz. With the dynamic pen control acti¬ vated, the pen tip does not oscillate when the pen force is set to zero. The pen tip floats vertically as though in zero G space, attached to a "rubber" tube support. The magnetic feedback forces which drive the pen tip are derived from a sum of currents representing the terms of a second order differential equation that governs the pen dynamics. These currents are generated in the com¬ puter so far as the constant pen force -F^ is con- cerned. The other currents are generated from the pen height signal d (by amplifiers and differentiating cir¬ cuits) . There is a spring compensation which may be generated by a spring compensation circuit 178 which may be an amplifier. The mass compensation component is generated by a circuit 180 which may include a double differentiating amplifier. The second order differen¬ tial equation that governs the dynamic pen control is:

F_h = kd + KW_N(l/g)d - P_i where: F_h is the magnetic lift force; F. is the lift force from the viscous ink flow which is acting on the pen; -F- is the pen force in the opposite direc¬ tion to the lift force) ; W_N is the weight equivalent of net effective dynamic pen mass; k is the spring σon- stant of the pen support and ink delivery tubes struc¬ ture 56; K is a lag constant which is less than but near unity (where 1/(1-K) is the acceleration force gain of the feedback system) ; g is the gravitational accelera¬ tion constant; and d is the vertical pen displacement. Inasmuch as the equilibrium position of the pen is taken at the rest position of the pen and flexural support structure 56 as determined by the weight of the pen and its support and the counter action against this weight of the magnetic attraction of the magnet to the core of the electromagnet, no constant weight term need be con¬ sidered in the second order differential equation given above.

It will be noted that the first term, kd, pro¬ duces a force that exactly balances the spring force when the pen is vertically displaced from its equili¬ brium position. The spring compensation circuitry 178 can compensate for any non-linearity due to the variable magnet gap between the magnet on the pen tip 28 and the electromagnet coil. The second term in the equation provides the force required for vertical acceleration of the pen tip. This term is only activated when writing over pre- fired lines, since accelerations required for following substrate camber are usually low. This term is effec- tively a force amplifier term which produces an acceler¬ ation force gain identified above. Oscillation will not occur as long as K is less than unity. The K value can be set by the operator for the amount of acceleration force gain desired. A suitable acceleration range has been found to be plus or minus 2g. As noted above, without the F_i term activated, the spring term, kd, completely eliminates the spring effect of the pen tip supporting structure. If the pen tip is set into oscil¬ lation while the electronics is turned off, the oscilla¬ tion is abruptly stopped when electronics is turned on, the pen tip again floating freely and remaining at any vertical level to which it is pushed. The F^_^ term provides constant, preset downward pen force which remains constant, even when following the vertical con¬ tours due to camber of the substrate surface. Typi¬ cally, for 4 and 8 mil wide lines, the pen force may vary between 50 and 250 milligrams, depending upon the ink material characteristics.

As discussed in connection with FIGS. 1, 11, 12 and 13 uniform line cross-sections are obtained on start of line by sensing the inception of ink flow, based on the rising pen height crossing a preset relative trigger height above the substrate. This output may be indepen¬ dent of the rate of pen rise. However, alternately, the system may be triggered to initiate table movement and increased ink flow at line start by sensing the upward vertical pen velocity at the inception of ink flow. This may be accomplished by differentiating the vertical displacement signal d, and when the differentiated ver¬ tical displacement signal corresponds to a preset velocity threshold, an output may be provided to repre¬ sent the start of ink flow. This output may in turn be used as the start signal to initiate table motion. At the present time the use of the preset relative trigger height threshold is preferred over pen lift velocity sensing. The velocity signal may be used to monitor

GMPI

/A* *^© vertical pen position deviations due to ink nonuniform- ity. The signal may be translated into an audible tone giving the operator a very useful monitor of ink quality during inking. Returning to FIGS. 12 and 13 it will be noted that interface controller 38 has a table motion pulse counter 190. The end of the table motion is computed as a function of the line length. The table motion pulses, which are provided by the table motor pulse generators 168 and 170 terminate at the end of a line. This is shown in the timing diagram depiction of the table motion pulses. As shown by the curve depicting the table motion in the timing diagram of FIG. 13, actual termination of table motion and actual termination of the line lags the end of the table motion pulses.

During this time lag the expansion of the ink must be accommodated in order to maintain uniformity of the line cross-section. This is accomplished by means of a delay circuit 192 and another control signal generator 194. The delay circuit 192 interposes an operator preset delay (OP₂) from the termination of the table command pulses until the control signal generator 194 is trig¬ gered to produce its control pulse. The duration of this control pulse may also be preset by the operator and is indicated OP-. At the leading edge of the pulse from the control signal generator 194, the ink pump motor controller 36 is reversed by utilizing the pulse as a reverse enable control. The pulses also apply to the pumping rate pulse generator 166 and increase the pump rate. Accordingly the ink pump is reversed to relieve the ink pressure which was main¬ tained during normal writing. The expansion of the ink upon termination is therefore compensated and line uni¬ formity maintained. At the end of the pulse from the - -

control signal generator 194 the ink pump rate is set to zero and pumping stops. The leading edge of the pulse from the control signal generator 124 also initiates pen lift and removes the pen force. The system shown in FIG. 12 may be implemented in the microprocessor con¬ troller by appropriate programming.

From the foregoing description it will be apparent that there has been provided an improved inking system which is especially suitable for computer aided design and computer aided manufacture of thick film hybrid circuits. While a preferred embodiment of the system has been described in order to elucidate the invention, variations and modifications of the herein described system, within the scope of the invention, will undoubtedly suggest themselves to those skilled in the art. Accordingly the foregoing description should be taken as illustrative and not in a limiting sense.

Claims

1. For use in producing patterns on a sub¬ strate with the aid of a member having an orifice, a system comprising means for moving said substrate with respect to said member, means for controllably feeding ink through said orifice at a volume rate synchronous with the rate of relative movement of said member and substrate, and means responsive to the viscous forces on the ink flowing from said orifice upon said substrate for dynamically controlling the vertical displacement of said member to maintain a constant thickness of line in said pattern for a given cross-sectional area of said line.

2. The invention as set forth in Claim 1 wherein said ink feeding means includes means for pump¬ ing ink through said orifice at a constant volume dis¬ placement rate.

3. The invention as set forth in Claim 2 wherein said pumping means has means for maintaining said ink in a closed volume out of which said ink is pumped to said member thereby minimizing storage of com¬ pression energy while said ink is pumped.

4. The invention as set forth in Claim 3 wherein said pumping means comprises a block having a pair of volumes for said ink, means for supplying ink to one of said volumes while pumping and delivering ink to said member from the other of said volumes and alter¬ nately supplying ink to the other of said volumes while pumping and delivering ink to said member from said one of said volumes.

5. The invention as set forth in Claim 4 wherein said supplying and pumping means comprises a four-way valve provided by a cylindrical valve body rotatable in an opening in said block, said block having a passage for the supply of ink, passages in said valve body for communicating said supply passage to one or the other of said volumes when said valve body is in differ¬ ent angular positions, said block having an outlet pas¬ sage communicating with said member opposed to said supply passage for alternately communicating with said volumes by way of said valve passages when said valve body is in said different angular positions, said valve body having an axial tapered aperture, and a tapered member disposed in said aperture expanding said valve body circumferentially to provide a zero clearance in said block opening.

6. The invention as set forth in Claim 5 wherein said tapered aperture is threaded and said expanding member is threaded into said tapered threaded aperture.

7. The invention as set forth in Claim 5 wherein said expanding member is a tapered metal pin.

8. The invention as set forth in Claim 4 wherein said pumping means comprises a pair of double acting displacement rams in pumping relationship with said volumes in said block, and means responsive to the displacement of said rams for reversing the direction of displacement thereof.

9. The invention as set forth in Claim 4 further comprising an assembly for supporting said member flexurally from said block and having a pair of tubes defining a triangle with a side of said block, said member being a pen tip interchangeably attached to the apex of said tubes, at least one of said tubes pro¬ viding a conduit for delivery of said ink to said member

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10. The invention as set forth in Claim 9 wherein an ink supply syringe is assembled to said block on the opposite side thereof from said tubes which pro¬ vide said flexural support to provide to a modular, interchangeable assembly of said block, syringe, pen tip, delivery and support tubes, and pumping means to enable rapid interchangeability of ink materials.

11. The invention as set forth in Claim 1 wherein said vertical displacement controlling means comprises means for compensating for the spring dis¬ placement force on said member.

12. The invention as set forth in Claim 1 further comprising means for applying acceleration forces for reducing the inertia of said member.

13. The invention as set forth in Claim 1 wherein said vertical displacement controlling means comprises electromagnetic means for vertically displac¬ ing said member and applying vertical forces thereto to lift and depress said member, means for sensing the dis¬ placement of said member, and means for applying feed¬ back forces to said member to satisfy the equation

F_h = kd + KW_N(l/g)'d - F , where: F. is the magnetic lift force; F. is the preselected lift force from the viscous ink flow; W_N is the weight equivalent of the net effective dynamic pen mass; k is the spring constant associated with said member; K is the lag or stability constant less than unity, where 1/(1-K) is the force gain of the system which applies forces to said member; g is the gravita¬ tional acceleration constant; and d is the vertical dis¬ placement of said member.

14. The invention as set forth in Claim 13 wherein said member is mounted on flexural support means, electro-optical means including a vane mounted on said flexural support means for providing an output signal corresponding to the vertical displacement of said member.

15. The invention as set forth in Claim 14 wherein said vane has an aperture therein, said electro- optical means including a junction photo transistor, and means for illuminating said photo transistor, said aper¬ ture being disposed to provide a path for said illumina¬ tion to said photo transistor when said member is lifted to full vertical displacement above said substrate.

16. The invention as set forth in Claim 1 further comprising means for varying the pressure of the ink supplied to said member at starts and terminations of the lines of the pattern thereby maintaining constant cross-section of line and compensating for compression and expansion of ink at said starts and terminations.

17. The invention as set forth in Claim 1 wherein said means for controlling vertical displacement includes means for providing a signal representing the movement of said member in the vertical direction, and means for initiating operation of said means for moving said substrate with respect to said member when said signal reaches a change in amplitude or rate of ampli¬ tude change thereof signifying the inception of ink flow.

18. In a system for writing patterns on a sub¬ strate with the aid of a pen member having an orifice, the improvement comprising means for moving said sub¬ strate with respect to said member, and means for σon- trollably feeding ink through said orifice at a volume rate synchronous with the rate of relative movement of said member and substrate.

19. The invention as set forth in Claim 18 wherein said ink feeding means includes means for pump¬ ing ink through said orifice at a constant volume dis¬ placement rate.

20. The invention as set forth in Claim 19 wherein said pumping means as means for maintaining said ink in a closed volume out of which said ink is pumped to said member thereby minimizing storage of compression energy while said ink is pumped.

21. The invention as set forth in Claim 20 wherein said pumping means comprises a block having a pair of volumes for said ink, means for supplying ink to one of said volumes while pumping and delivering ink to said member from the other of said volumes and alter¬ nately supplying ink to the other of said volumes while pumping and delivering ink to said member from said one of said volumes.

22. The invention as set forth in Claim 21 wherein said supplying and pumping means comprises a four-way valve provided by a cylindrical valve body rotatable in an opening in said block, said block having a passage for the supply of ink, passages in said valve body for communicating said supply passage to one or the other of said volumes when said valve body is in differ¬ ent angular positions, said block having an outlet pas¬ sage communicating with said member opposed to said supply passage for alternately communicating with said volumes by way of said valve passages when said valve body is in said different angular positions, said valve body having an axial tapered aperture, and a tapered member disposed in said aperture expanding said valve body σircumferentially to provide a zero clearance in said block opening.

23. The invention as set forth in Claim 22 wherein said tapered aperture is threaded and said expanding member is threaded into said tapered threaded aperture.

24. The invention as set forth in Claim 22 wherein said expanding member is a tapered metal pin.

25. The invention as set forth in Claim 20 wherein said pumping means comprises a pair of double acting displacement rams in pumping relationship with said volumes in said block, and means responsive to the displacement of said rams for reversing the direction of displacement thereof.

26. The invention as set forth in Claim 20 further comprising an assembly for supporting said member flexurally from said block and having a pair of tubes defining a triangle with a side of said block, said member being a pen tip interchangeably attached to the apex of said tubes, at least one of said tubes pro¬ viding a conduit for delivery of said ink to said member,

27. The invention as set forth in Claim 26 wherein an ink supply syringe is assembled to said block on the opposite side thereof from said tubes which pro¬ vide said flexural support to provide to a modular, interchangeable assembly of said block, syringe, pen tip, delivery and support tubes, and pumping means to enable rapid interσhangeability of ink materials.

28. The invention as set forth in Claim 18 further comprising means for varying the pressure of the ink supplied to said member at starts and terminations of the lines of the pattern thereby maintaining constant cross-section of line and compensating for compression and expansion of ink at said starts and terminations.

29. In a system for writing patterns on a substrate with the aid of a pen member having an ori¬ fice, the improvement comprising a flexural support for said pen member enabling vertical displacement thereof with respect to said substrate, and means responsive to the viscous forces of the ink flowing from said orifice upon said substrate for dynamically controlling the ver¬ tical displacement of said member to maintain a constant thickness of line in said pattern for a given cross- sectional area of said line.

30. The invention as set forth in Claim 29 wherein said vertical displacement controlling means comprises means for compensating for the spring dis¬ placement force on said member.

31. The invention as set forth in Claim 29 further comprising means for applying acceleration forces for reducing the inertia of said member.

32. The invention as set forth in Claim 29 wherein said vertical displacement controlling means comprises electromagnetic means for vertically displac¬ ing said member and applying vertical forces thereto to lift and depress said member, means for sensing the dis¬ placement of said member, and means for applying feed¬ back forces to said member to satisfy the equation

F_h = kd + KW_N(l/g)d - F_t, where: F_h is the magnetic lift force, F^ is the preselected lift force from the viscous ink flow; _N is the weight equivalent of the net effective dynamic pen mass; k is the spring constant associated with said member; K is the lag or stability constant less than unity, where 1/(1-K) is the force gain of the system which applies forces to said member; g is the gravita¬ tional acceleration constant; and d is the vertical dis¬ placement of said member.

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33. The invention as set forth in Claim 32 wherein said member is mounted on flexural support means, electro-optical means including a vane mounted on said flexural support means for providing an output signal corresponding to the vertical displacement of said member.

34. The invention as set forth in Claim 32 wherein said vane has an aperture therein, said electro- optical means including a junction photo transistor, and means for illuminating said photo transistor, said aper¬ ture being disposed to provide a path for said illumina¬ tion to said photo transistor when said member is lifted to full vertical displacement above said substrate.

35. The invention as set forth in Claim 29 wherein said system includes means for moving said sub¬ strate with and pen member with respect to each other, and said means for controlling vertical displacement includes means for providing a signal representing the movement of said member in the vertical direction, and means for initiating operation of said means for moving said substrate with respect to said member when said signal reaches a change in amplitude or rate of ampli¬ tude change signifying the inception of ink flow through said orifice.